1. Field of the Invention
The present invention relates to an imaging device in which a lens driving system is controlled during imaging, and to a method for driving an optical system.
2. Description of the Related Art
Recently, camera drive systems of the open-loop control method in which a stepping motor serves as an actuator have been widespread. Such a control mechanism provides high positioning resolution and achieves high positioning accuracy on the order of several micrometers (μm).
In one known camera drive system, when a motor drives a lens, an operation control unit detects the state of an operating member and controls the motor according to the detected state or the calculated amount. The operating member is implemented as, for example, a lever/ring the middle of whose operating range is the natural restoration point (see Japanese Unexamined Patent Application Publication No. 59-216111) or a rotating ring (see Japanese Unexamined Patent Application Publication No. 63-177118). Such control performed by the operation control unit improves the positioning accuracy with which the lens is controlled; and the need for rings that allow for a higher-resolution operation has increased.
In lens mechanisms (typically used for business purposes, etc.) in which a ring and a lens are mechanically connected and the lens moves forward or backward in a lens barrel depending on the amount of rotation of the ring, the angle of rotation of the ring is limited in association with the maximum forward or backward position of the lens in the lens barrel. In addition, the angle of rotation of the ring and the lens position are in one-to-one correspondence. Such lens mechanisms are therefore intuitive and easy-to-operate.
Lens position detection systems with a resolution as high as operating rings also have been demanded.
Existing lens position determination methods include the following types.
A first type is the type in which the absolute position is determined using a hall sensor, a potentiometer, or the like.
A second type is the type in which with the use of a reset sensor for detecting a reference position and a frequency generator (FG) pulse counter for counting pulses from the reference position, or the reset sensor and a magnetoresistive (MR) sensor, or the like, the relative position from the reference position is determined using the reset sensor/encoder combination (see Japanese Unexamined Patent Application Publication No. 59-216111, noted above).
A third type is the in which that a plurality of reference positions are detected using a plurality of reset sensors, e.g., two reset sensors, three reset sensors, etc.